CN114354036B - Method and device for synchronously measuring surface pressure and three-dimensional shape of motion model - Google Patents
Method and device for synchronously measuring surface pressure and three-dimensional shape of motion model Download PDFInfo
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- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
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Abstract
The invention relates to a method for synchronously measuring surface pressure and three-dimensional morphology of a motion model, which comprises the following steps: preparing the same pressure-sensitive paint on the surfaces of the test model and the calibration sample; performing binocular calibration on the test model by adopting two cameras to obtain system parameters; the method comprises the following steps of (1) launching a test model, synchronously triggering a pulse laser and one camera, sending a pulse laser beam and exciting a pressure-sensitive paint, shooting a first image, delaying to trigger the other camera, and shooting a second image; matching the two images, calculating three-dimensional coordinates pixel by pixel, and calculating the ratio of the light intensity values of the two images pixel by pixel; and calibrating the pressure sensitivity of the sample to obtain a light intensity ratio-pressure calibration curve, calculating the pressure value corresponding to the light intensity ratio of the test model pixel by pixel, and obtaining the three-dimensional coordinates and the pressure value of each pixel point on the surface of the model. Compared with the prior art, the method can realize the synchronous measurement of the surface pressure and the three-dimensional shape of the high-speed motion model in a non-contact manner, high spatial resolution and high efficiency manner.
Description
Technical Field
The invention relates to the technical field of high-speed motion model pneumatic thermodynamic measurement, in particular to a method and a device for synchronously measuring the pressure and three-dimensional morphology of a motion model.
Background
The Pressure Sensitive Paint (PSP) technology is a non-contact optical flow field measurement technology with high spatial resolution developed by utilizing the oxygen quenching effect of luminescent probe molecules in an excited state. The technology prepares the pressure-sensitive paint on the surface of a test model, when a coating is excited by ultraviolet light, the coating image is collected by image collecting equipment such as a CCD camera, and the pressure field on the surface of the model is reconstructed by analyzing the characteristics of the pressure-sensitive paint such as light intensity, luminescence life and the like through image processing.
In recent years, pressure sensitive paint technology has been widely used in wind tunnel testing and flight test research. In the experimental research of the aerothermodynamics of a motion model, the traditional test method based on measuring instruments such as a pressure sensor is difficult to develop due to the problems of signal transmission and the like, and the pressure-sensitive paint technology shows obvious advantages. However, for high speed motion models, two major challenges are presented to the development of pressure sensitive paint tests.
When the mold is in high-speed motion, if a pressure-sensitive paint measurement method based on light intensity is used, measurement errors are introduced by changes in the excitation light field during the motion of the mold. In addition, the intensity method has long image acquisition time, the image has serious motion blur, and the quality of image data is reduced. On the other hand, in the aerodynamic thermodynamic research of a motion model, the surface pressure of the model often shows obvious relevance with the motion attitude, the deformation and the like, so that the three-dimensional shape information obtained in the synchronization of the measurement of the pressure parameters of the model has important value for the analysis of the fluid-solid coupling characteristic of the test model. In the existing experimental research, a three-dimensional measurement system is usually adopted to capture the spatial attitude and the morphology of a model, and the three-dimensional measurement system is mutually independent from the pressure measurement system, so that synchronous measurement is difficult to realize.
In recent years, researchers pay attention to the synchronous measurement technology of three-dimensional morphology, posture and pressure field of a high-speed motion model, and several new methods are proposed:
a paper 'Single-shot, lifetime-based pressure-sensitive-paint for reflecting blanks' published in journal 'measuring Science and Technology' proposes a pressure-sensitive paint measuring method based on a Single-pulse life method, wherein two images are continuously recorded by using a cross-frame camera at the stage of paint light intensity attenuation, and are used for representing a luminous life value, and the pressure is calculated according to the two images. The method is well applied to the surfaces of impeller machines such as a rotor wing, and the upper limit of the speed of the motion model pressure sensitive paint measurement is increased to about 300m/s. However, this technique and experimental apparatus do not completely solve the problem of image motion blur at higher speeds. Because the second frame of the frame-crossing camera is exposed in an open mode, the shutter exposure time is long, when the model motion speed is higher (> 1000 m/s), the second frame image has serious motion blur, the data quality is greatly reduced, and a measurement error is introduced. In addition, the method can only obtain two-dimensional image information, and cannot obtain three-dimensional data of the model synchronously.
Chinese invention patent CN 112066912A discloses a method and a device for synchronously measuring a three-dimensional surface profile and a surface pressure of a model by using a projection structured light and pressure sensitive paint technology, however, the method uses a phase measurement mode based on a phase shift method, and a plurality of images require a long acquisition time, so that the method is not suitable for application of a motion model. In addition, in the method, the fringe phase information is influenced by pressure pulsation, so that the local phase is distorted, and the three-dimensional measurement precision is reduced.
"Simultaneous Measurement of surface shape and compression using structured projection" published in journal "Measurement Science and Technology" proposes projecting a speckle pattern using a modified ultraviolet LCD projector and reconstructing three-dimensional coordinates of the model using a binocular system. The method still uses a pressure-sensitive paint data acquisition method based on a strength method, and is not suitable for motion model measurement.
A rotor wing space attitude and pressure measuring method based on a binocular vision system and grid pressure sensitive paint is provided by a paper 'Simulanous pressure and deformation field on promoter used' published in journal 'MEASUREMENT'.
In summary, in the research of the aerodynamic thermomechanical test, the synchronous measurement of the surface pressure, the three-dimensional shape and the attitude of the motion model is challenging, and the development of a corresponding measurement method and a corresponding measurement device is significant.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a non-contact high-spatial-resolution and high-efficiency synchronous measurement method and device for the pressure and the three-dimensional shape of a motion model.
The purpose of the invention can be realized by the following technical scheme:
according to one aspect of the invention, a method for synchronously measuring surface pressure and three-dimensional topography of a motion model is provided, which comprises the following steps:
s1: preparing the same pressure-sensitive paint on the surfaces of the test model and the sample for pressure sensitivity calibration respectively;
s2: forming a binocular image acquisition system by adopting two cameras, and carrying out binocular calibration on the test model to obtain system calibration parameters;
s3: the test model is transmitted to enable the test model to be in a free flight state, a pulse laser and one camera are synchronously triggered according to time sequence control, a pulse laser beam is emitted and projected to the test model to excite the pressure-sensitive paint, a first image is shot, the other camera is triggered in a delayed mode, and a second image is shot;
s4: matching the first image and the second image according to the speckle characteristics of the images, reconstructing three-dimensional coordinates of a test model according to the system calibration parameters, and calculating the ratio of light intensity values of the two images pixel by pixel according to a pixel point mapping relation established by an image matching result;
s5: carrying out pressure sensitivity calibration on a sample prepared with the pressure sensitive paint by using a pressure calibration system to obtain a light intensity ratio-pressure calibration curve;
s6: and calculating the pressure value corresponding to the light intensity ratio of the test model point by point according to the light intensity ratio-pressure calibration curve, and finally obtaining the three-dimensional coordinates and the pressure value of each pixel point on the surface of the model so as to realize the synchronous measurement of the three-dimensional morphology and the pressure distribution.
Preferably, the pulse laser beam sequentially passes through the ground glass diffusion sheet and the central line of the projection lens to form a large-area surface light source projection with a speckle pattern and cover the surface of the test model so as to excite the pressure-sensitive paint on the surface of the test model.
Preferably, the exposure time of the two cameras is the same, both 1 to 10 μ s.
Preferably, the photographing time of the second image differs from the photographing time of the first image by 1 to 10 μ s.
Preferably, the S5 includes the steps of:
s5.1: placing the sample prepared with the pressure sensitive paint in the S1 in a pressure calibration cabin provided with a glass window;
s5.2: acquiring two pressure-sensitive paint sample images by using the same time sequence and image acquisition method as S3;
s5.3: adjusting the pressure in the pressure calibration cabin to a target pressure value, respectively taking square areas with the same side length near the central points of the two pressure-sensitive paint sample images, averaging the pixel light intensity values in the square areas, and dividing the average light intensity values to obtain light intensity ratio values under the target pressure value;
s5.4: and repeating S5.3, obtaining a plurality of groups of pressure-light intensity ratio data, covering the test range with the calibrated pressure range, and drawing a light intensity ratio-pressure calibration curve according to all the pressure-light intensity ratio data.
According to another aspect of the present invention, there is provided a synchronous measurement apparatus for implementing the method for synchronously measuring surface pressure and three-dimensional topography of a motion model, so as to synchronously measure surface pressure and three-dimensional topography of a test model, comprising:
a signal generator: for generating a trigger signal;
a delay pulse generator: to achieve synchronization and delay of the trigger signal;
an excitation light module: the surface light is used for generating pulse excitation light and forming speckle patterns which are uniformly distributed and is projected to the test model;
an image measurement module: the system is used for carrying out binocular calibration, obtaining system calibration parameters and capturing the excited pressure-sensitive paint luminous image;
a computer: for storing the images captured by the image measurement module and the acquired system calibration parameters.
Preferably, the excitation light module comprises a pulse laser, a ground glass diffusion sheet and a projection lens which are sequentially arranged, wherein the pulse laser emits a pulse laser beam, a small-area surface light source with speckle patterns is formed by modulation of the ground glass diffusion sheet, a large-area surface light source with large speckle patterns is formed by beam expansion of the projection lens, the surface light source covers the surface of the test model, and then the pressure-sensitive paint on the surface of the test model is excited.
Preferably, the pulse laser emits a pulse laser wavelength of 200-1000 nm and a pulse energy range of 1 mJ-1000 mJ.
Preferably, the image measuring module comprises a first camera and a second camera, and an imaging lens and an optical filter for filtering exciting light and only retaining a fluorescence signal of the pressure-sensitive paint are arranged on the first camera and the second camera.
Compared with the prior art, the invention has the following advantages:
(1) The invention can realize the synchronous measurement of the non-contact pressure and the space three-dimensional appearance of a high-speed motion model, namely a motion model with the motion speed of 100-2000 m/s by adopting a set of measuring device, namely, the one-time image data acquisition is carried out at a certain moment in the motion process of the same model, and the transient pressure on the surface of the model, the three-dimensional appearance and the space posture are reconstructed by data processing.
(2) According to the invention, a large-area surface light source containing large speckle patterns is generated by using a modulation light path consisting of a pulse laser, a ground glass diffusion sheet and a projection lens, and is projected to the surface of a measurement model to excite the pressure-sensitive paint, so that the same speckle patterns exist in a luminous image of the pressure-sensitive paint, and the speckle patterns can meet the energy requirement of the pressure-sensitive paint in the area of a speckle dark part on the intensity of excitation light, thereby ensuring the effective excitation of the pressure-sensitive paint in a global range, realizing full-field pressure measurement, avoiding the complexity of directly marking the surface of the pressure-sensitive paint and the loss of local signals of marking points, and ensuring the integrity of full-field pressure data.
(3) According to the invention, two cameras are used for image shooting, the exposure starting time of one camera is delayed, the ratio of the light intensities of the two images is obtained, the change of the luminous life of the pressure-sensitive paint can be reflected, and the pressure value is further obtained by using the system calibration parameters. Because the two images are both from the excitation of the same pulse laser to the pressure-sensitive paint, the method is insensitive to the change of the space light intensity distribution of the excitation light in the moving process of the model, namely has the self-reference characteristic and is suitable for the pressure-sensitive paint measurement of the moving model.
(4) The invention reduces the blurring of the moving model image to the maximum extent by using two cameras to acquire the pressure-sensitive paint image in limited short-time exposure.
Drawings
FIG. 1 is a flowchart illustrating a method for synchronously measuring surface pressure and three-dimensional topography of a motion model according to an embodiment of the present invention;
FIG. 2 is a timing diagram of the embodiment shown in FIG. 1;
FIG. 3 is a schematic structural diagram of a testing apparatus for implementing the embodiment shown in FIG. 1;
labeled as: 1. a signal generator; 2. a delay pulse generator; 3. a pulsed laser; 4. a ground glass diffusion sheet; 5. a projection lens; 6. testing the model; 7. a computer; 8. a camera number one; 9. a second camera; 10. an imaging lens; 11. and (3) a filter.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.
Referring to fig. 1, the present embodiment provides a method for synchronously measuring surface pressure and three-dimensional topography of a motion model, including the following steps:
s1: respectively preparing the same pressure-sensitive paint solution on the surface of the test model 6 and the surface of the sample for pressure sensitivity calibration;
as an alternative embodiment, the pressure-sensitive paint solution is porous ceramic substrate pressure-sensitive paint containing a pentafluortetraphenylporphyrin platinum probe, and the pressure-sensitive paint is uniformly sprayed on the surface of the test model 6 by using a compressed air spray pen; the pressure sensitive paint sample adopts aluminum sheets.
S2: and forming a binocular image acquisition system by adopting two cameras, and carrying out binocular calibration on the test model to obtain system calibration parameters.
S3: the method comprises the steps of launching a test model to enable the test model to be in a free flight state, synchronously triggering a pulse laser and a first camera 8 according to a system time sequence, sending a pulse laser beam and projecting the pulse laser beam to the test model to excite the pressure-sensitive paint, shooting a first image, delaying triggering a second camera 9 and shooting a second image;
as an alternative embodiment, a first camera 8 and a second camera 9 are adopted to form an image measuring module, both the cameras are provided with an imaging lens 10 and an optical filter 11, and the optical filter 11 is used for filtering exciting light and only retaining fluorescence signals of the pressure-sensitive paint. And respectively adjusting the spatial positions of the first camera 8 and the second camera 9, so that the visual field overlapping regions of the two cameras cover the test model, and further carrying out binocular calibration on the test model to obtain system calibration parameters.
A modulation light path consisting of a pulse laser 3, a ground glass diffusion sheet 4 and a projection lens 5 is used for emitting a pulse laser beam, the light path is adjusted, so that the pulse laser beam sequentially passes through the center lines of the ground glass diffusion sheet 4 and the projection lens 5, when the pulse laser beam passes through the ground glass diffusion sheet 4, a small-area light source with speckle patterns is formed, then the pulse laser beam is expanded by the projection lens 5 to form a large-area surface light source with large speckle patterns, the large-area surface light source covers the surface of a test model 6, and further the pressure-sensitive paint on the surface of the test model 6 is excited;
referring to fig. 2, the signal generator 1 is used to control the system timing sequence, two paths of synchronous TTL signals are generated to trigger the pulse laser 3 and the first camera 8 at the same time, the pulse laser 3 emits a beam of pulse laser, and the first camera 8 captures a first image. And generating a delayed TTL signal by using the delay pulse generator 2, and triggering the second camera 9 to shoot a second image.
Specifically, the exposure time of the first camera 8 and the second camera 9 is the same, and is 1 to 10 μ s.
Specifically, the signal delay time of the delay pulse generator 2 is 1 to 10 μ s.
In this embodiment, the camera exposure time is 5 μ s and the signal delay time is 3 μ s.
S4: performing image matching on the first image and the second image according to the speckle characteristics of the images, reconstructing three-dimensional morphology information of the test model according to system calibration parameters, and calculating the ratio of light intensity values of the two images pixel by pixel according to a pixel point mapping relation established by an image matching result;
s5: carrying out pressure sensitivity calibration on a sample prepared with the pressure sensitive paint by using a pressure calibration system to obtain a light intensity ratio-pressure calibration curve;
s5.1: placing the sample prepared with the pressure-sensitive paint in the S1 in a pressure calibration cabin provided with a glass window;
s5.2: acquiring two pressure-sensitive paint sample images by using a time sequence and image acquisition system which are the same as those of S2;
s5.3: adjusting the pressure in the pressure calibration cabin to a target pressure value, respectively taking square areas with the side length of L near the center points of the two pressure-sensitive paint sample images, averaging the pixel light intensity values in the square areas, and dividing the average light intensity values to obtain light intensity ratio values under the target pressure value;
as an alternative embodiment, the side length L of the square is 20 pixels.
S5.4: and repeating S5.3 to obtain multiple groups of pressure-light intensity ratio data, enabling the calibrated pressure range to cover the test range, and drawing a light intensity ratio-pressure calibration curve according to all the pressure-light intensity ratio data.
S6: and calculating the pressure value corresponding to the light intensity ratio of the test model point by point according to the light intensity ratio-pressure calibration curve, and finally obtaining the three-dimensional coordinates and the pressure value of each pixel point on the surface of the model so as to realize the synchronous measurement of the three-dimensional morphology and the pressure distribution.
Referring to fig. 3, the present embodiment further provides a measurement apparatus for implementing a method for synchronously measuring a surface pressure and a three-dimensional topography of a motion model, so as to synchronously measure the surface pressure and the three-dimensional topography of a test model 6, including:
signal generator 1: for generating a trigger signal;
delay pulse generator 2: to achieve synchronization and delay of the trigger signal;
an excitation light module: the device comprises a pulse laser 3, a ground glass diffusion sheet 4 and a projection lens 5 which are sequentially arranged, wherein the pulse laser 3 emits a pulse laser beam, a small-area light source with speckle patterns is formed by modulation of the ground glass diffusion sheet 4, and then a large-area surface light source with large speckle patterns is formed after beam expansion through the projection lens 5 to cover the surface of the test model 6, so that pressure-sensitive paint on the surface of the test model 6 is excited; the 4 meshes of the ground glass diffusion sheet are 1000-3000; the focal length of the projection lens 5 is 20-100 mm.
Specifically, the wavelength of the pulse laser is 200-1000 nm, and the pulse energy range is 1 mJ-1000 mJ. In this embodiment, a pulse laser with a wavelength of 532nm and a pulse energy of 300mJ is specifically used to ensure that a higher signal-to-noise ratio can still be obtained when an image is taken within a shorter exposure time.
An image measurement module: the system is used for carrying out binocular calibration, obtaining system calibration parameters and capturing the excited pressure-sensitive paint luminous image; the system comprises a first camera 8 and a second camera 9, wherein the number of camera pixels is 100 Mp-8000 Mp; the first camera 8 and the second camera 9 are both provided with an imaging lens 10 and an optical filter 11, the focal length of the imaging lens 10 is 20-100 mm, and the aperture value f is 1.2-5.6.
The computer 7: for storing the images captured by the image measurement module and the acquired system calibration parameters.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.
Claims (9)
1. A synchronous measurement method for surface pressure and three-dimensional topography of a motion model is characterized by comprising the following steps:
s1: preparing the same pressure-sensitive paint on the surfaces of the test model and the sample for pressure sensitivity calibration respectively;
s2: forming a binocular image acquisition system by adopting two cameras, and carrying out binocular calibration on the test model to obtain system calibration parameters;
s3: the test model is transmitted to enable the test model to be in a free flight state, a pulse laser and one camera are synchronously triggered according to time sequence control, a pulse laser beam is emitted and projected to the test model to excite the pressure-sensitive paint, a first image is shot, the other camera is triggered in a delayed mode, and a second image is shot;
s4: matching the first image and the second image according to the speckle characteristics of the images, reconstructing three-dimensional coordinates of the test model according to the calibration parameters of the system, and calculating the ratio of light intensity values of the two images pixel by pixel according to a pixel point mapping relation established by the image matching result;
s5: carrying out pressure sensitivity calibration on a sample prepared with the pressure sensitive paint by using a pressure calibration system to obtain a light intensity ratio-pressure calibration curve;
s6: and calculating the pressure value corresponding to the light intensity ratio of the test model point by point according to the light intensity ratio-pressure calibration curve, and finally obtaining the three-dimensional coordinates and the pressure value of each pixel point on the surface of the model so as to realize the synchronous measurement of the three-dimensional morphology and the pressure distribution.
2. The method as claimed in claim 1, wherein the pulsed laser beam passes through a ground glass diffuser and a central line of a projection lens in sequence to form a large area light source projection with speckle pattern and cover the surface of the test model, so as to excite the pressure sensitive paint on the surface of the test model.
3. The method for synchronously measuring the surface pressure and the three-dimensional topography of the motion model according to claim 1, wherein the exposure time of the two cameras is the same and is 1-10 μ s.
4. The method for synchronously measuring the surface pressure and the three-dimensional topography of the motion model as claimed in claim 3, wherein the difference between the shooting time of the second image and the shooting time of the first image is 1-10 μ s.
5. The method for synchronously measuring the surface pressure and the three-dimensional topography of the motion model according to claim 1, wherein the step S5 comprises the following steps:
s5.1: placing the sample prepared with the pressure sensitive paint in the S1 in a pressure calibration cabin provided with a glass window;
s5.2: acquiring two pressure-sensitive paint sample images by using the same time sequence and image acquisition method as S3;
s5.3: adjusting the pressure in the pressure calibration cabin to a target pressure value, respectively taking square areas with the same side length near the central points of the two pressure-sensitive paint sample images, averaging the pixel light intensity values in the square areas, and dividing the average light intensity values to obtain a light intensity ratio value under the target pressure value;
s5.4: and repeating S5.3, obtaining a plurality of groups of pressure-light intensity ratio data, covering the test range with the calibrated pressure range, and drawing a light intensity ratio-pressure calibration curve according to all the pressure-light intensity ratio data.
6. A synchronous measurement device for implementing a synchronous measurement method of surface pressure and three-dimensional topography of a motion model according to any one of claims 1 to 5, for synchronously measuring the surface pressure and the three-dimensional topography of a test model (6), comprising:
signal generator (1): for generating a trigger signal;
delay pulse generator (2): to achieve synchronization and delay of the trigger signal;
an excitation light module: the surface light used for generating the pulse exciting light and forming the speckle pattern to be uniformly distributed is projected to the test model (6);
an image measurement module: the system is used for carrying out binocular calibration, obtaining system calibration parameters and capturing the excited pressure-sensitive paint luminous image;
computer (7): for storing the images captured by the image measurement module and the acquired system calibration parameters.
7. The synchronous measuring device of claim 6, wherein the excitation light module comprises a pulse laser (3), a ground glass diffusion sheet (4) and a projection lens (5) which are arranged in sequence, the pulse laser (3) emits a pulse laser beam, a small-area surface light source with speckle patterns is formed by modulation of the ground glass diffusion sheet (4), and then the pulse laser beam is expanded by the projection lens (5) to form a large-area surface light source with large speckle patterns, and the large-area surface light source covers the surface of the test model (6), so that the pressure-sensitive paint on the surface of the test model (6) is excited.
8. The synchronous measuring device according to claim 7, wherein the pulse laser (3) emits a pulse laser wavelength of 200-1000 nm and a pulse energy range of 1-1000 mJ.
9. The synchronous measuring device according to claim 6, wherein the image measuring module comprises a first camera (8) and a second camera (9), and an imaging lens (10) and a filter (11) for filtering exciting light and only retaining fluorescence signals of the pressure sensitive paint are arranged on the first camera (8) and the second camera (9).
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